(Originally, nth was defined in Emacs Lisp in subr.el,
but its definition was redone in C in the 1980s.)

The nth function returns a single element of a list.
This can be very convenient.

Note that the elements are numbered from zero, not one. That is to
say, the first element of a list, its CAR is the zeroth element.
This is called ‘zero-based’ counting and often bothers people who
are accustomed to the first element in a list being number one, which
is ‘one-based’.